Catalytic converters reduce exhaust gas emissions in vehicles using an internal combustion engine. A three-way catalytic converter includes a substrate with a coating of catalyst materials that stimulate the oxidation of hydrocarbon and carbon monoxide, and the reduction of nitrogen oxides, in the exhaust gas. The catalysts operate optimally when the temperature of the catalysts is above a minimum level and when the air/fuel ratio is stoichiometric. Stoichiometry is defined as an ideal air/fuel ratio, which is 14.7 to 1 for gasoline.
It is desirable to optimize the air/fuel ratio in the engine for performance as well as emissions control. Emissions control is increasingly difficult at startup because the catalysts have not reached the warmed-up operating temperature. There are numerous factors that affect cold start emissions but they may be summarized in two major categories. The first is engine-out emissions and the second is catalyst efficiency. Engine-out emissions are primarily dependant on base engine design, production and function of the engine control system. Catalyst efficiency is directly related to converter temperature for a given converter as designed. Catalyst light-off is defined as true when the emission conversion efficiency exceeds 50%.
One way to speed up catalyst converter warm-up or shorten its light-off time at an engine cold start is to generate high engine-out energy. The energy is mainly dependent on exhaust temperature and mass flow rate while the exhaust gas specific heat capacity does not vary much. Retarding ignition timing and increasing engine idle speed are known engine control methods to reduce cold start emissions. On-board diagnostics version 2 (OBDII) regulations require cold start emissions reduction control strategies to be monitored and that the target conditions necessary to reduce emissions or catalyst light-off time are achieved and emissions do not exceed 1.5 times the applicable FTP (Federal Test Procedures) standards.